Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$250.55	12.478%	$281.8136	$281.81	$281.80	$281.80
Purchase #2	$139.92	7.811%	$150.8492	$150.85	$150.85	$150.80
Purchase #3	$53.78	3.737%	$55.7898	$55.79	$55.80	$55.80
Purchase #4	$187.57	4.669%	$196.3276	$196.33	$196.35	$196.30
Purchase #5	$122.27	13.115%	$138.3057	$138.31	$138.30	$138.30
Purchase #6	$111.83	11.367%	$124.5417	$124.54	$124.55	$124.50
Purchase #7	$6.40	3.767%	$6.6411	$6.64	$6.65	$6.60
7 purchase totals =	$872.32		$954.2687	$954.27	$954.30	$954.10